(E)-N-Benzyl­idene-3-chloro-4-fluoro­aniline

The title mol­ecule, C₁₃H₉ClFN, is substantially planar. The phenyl and 3-chloro-4-fluoro­phenyl rings are on opposite sides of the C=N bond. There is an intermolecular C-H...F short contact with a C...F distance of 3.348 (2) Å and a C-H...F angle of 137.4 (1)°. The mol­ecules are held in layers parallel to the bc plane.

S1. Comment

The title compound, (I), belongs to the family of fluorine-substituted benzylidene anilines. It displays anti-inflammatory activity in mice (Nargund & Srinivasmurthy, 1994) and has been found to orient butadienes, styryl coumarins for photodimerization, and also not to accept hydrogen bonds. Interest in these compounds has stemmed from the fact that they are useful models in the development of the principles of crystal engineering (Guru Row, 1999). It has been pointed out that organofluorine has low proton affinity (Dunitz & Taylor, 1997; Shimoni & Glusker, 1994) and hardly accepts hydrogen bonds. Introduction of fluorine in organic molecules has been found to enhance crystal densities and solid-state photochemical reactivity (Vishnumurthy et al., 1996). In light of the above observations, we are currently involved in analysing structures which contain fluorine as a substituent to explore the types of weak interactions fluorine can form in drugs and drug intermediates. The crystal structure of the title compound, (I), has been determined in this regard.

The C atoms in (I) are in a state of sp² hybridization and there are no significant deviations except the angles at C1; C2—C1—N 124.8 (1)° and C6—C1—N 116.2 (1)°. This variation is reflected in the distances of nitrogen from corresponding H atoms; the interatomic N···H2 bond distance of 2.695 (2) Å is greater than N···H6 of 2.512 (2) Å.

The C1—N single-bond distance of 1.416 (2) Å is expectedly longer than the C7═N double-bond distance of 1.249 (2) Å. The C7—C1' bond distance of 1.466 (2) Å is also longer than the expected value and these variations keep interelectronic repulsions to the minimum.

The larger C3—Cl bond distance of 1.731 (2) Å also minimizes the repulsion between the ortho-substituted fluorine and also reduces the dipole–dipole repulsive forces.

The bond lengths associated with the bridging atoms C1—N—C7—C1' are of significance in reflecting the effects of substituents present in the aniline benzylidene ring. The torsion angle C1—N—C7—C1' of −177.4 (2)° indicates the antiperiplanar disposition of the two phenyl rings. The atoms H7 and C1 are cis with respect to each other about C7—N, and H7 and C2' are anti with respect to each other [C1—N—C7—H7 2.6 (3)° and C2'—C1'—C7—H7 178.5 (2)°]

The F and Cl atoms attached to the aniline ring have deviations of 0.022 (1) and 0.044 (1) Å, respectively. An important factor in the solid-state molecular configuration and the twisting of the aniline & benzylidene rings from the C1—N—C7—C1' plane which has been observed in benzylidene anilines (Burgi & Dunitz, 1969) but it is interesting that in case of the title compound, the entire molecule is planar. The geometry and planarity of the molecule indicates a close spatial proximity between H2' and N and the observed distance is 2.593 (2) Å. It is also interesting to note that the two ortho-H atoms H2 and H2' are almost equidistant [2.651 (2) and 2.657 (2) Å, respectively] from the azomethine C7 atom. The hydrogen bond C4'—H4'···F [3.348 (2) Å, angle 137.4 (1)°] is a weak bond with a marginal H4'···F bond distance value of 2.603 (1) Å. The molecules are held in parallel layers in the bc plane.

S2. Experimental

The title compound was synthesized by the reaction of 3-chloro-4-fluoroaniline dissolved in absolute ethanol (30 ml). Benzaldehyde (0.01 M) was added and this mixture was refluxed gently for 3 h in the presence of 2–3 drops of glacial acetic acid. Afterwards, the reaction mixture was cooled to room temperature and poured onto crushed ice. The precipitate obtained was filtered, washed with ice-cooled water, dried in air and finally recrystallized from dimethylformamide.

S3. Refinement

The H-atom positional parameters were calculated geometrically and fixed with U_iso(H) = 1.2U_eq(parent atom).

Computing details

Data collection: CAD-4-PC (Enraf–Nonius, 1993); cell refinement: CAD-4-PC; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: SHELXL97.

N-arylenamine-3-chloro-4-fluoroaniline

Crystal data

C13H9ClFN	Dx = 1.409 Mg m^−3 Dm = 1.408 Mg m^−3 Dm measured by flotation
Mr = 233.66	Melting point: (39+273) K
Monoclinic, P21/c	Cu Kα radiation, λ = 1.54180 Å
a = 5.7874 (7) Å	Cell parameters from 25 reflections
b = 7.5327 (7) Å	θ = 30–40°
c = 25.3418 (19) Å	µ = 2.94 mm^−1
β = 94.227 (8)°	T = 293 K
V = 1101.76 (19) Å^3	Needle, pale yellow
Z = 4	0.2 × 0.1 × 0.1 mm
F(000) = 480

Data collection

Nonius CAD-4 diffractometer	Rint = 0.024
Radiation source: fine-focus sealed tube	θmax = 69.9°, θmin = 3.5°
Graphite monochromator	h = 0→7
ω–2θ scans	k = 0→9
2285 measured reflections	l = −30→30
2082 independent reflections	2 standard reflections every 60 min
1798 reflections with I > 3σ(I)	intensity decay: 1%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.035	H-atom parameters not refined
wR(F^2) = 0.123	Calculated w = 1/[σ^2(Fo^2) + (0.0776P)^2 + 0.2845P] where P = (Fo^2 + 2Fc^2)/3
S = 0.98	(Δ/σ)max = 0.016
2082 reflections	Δρmax = 0.16 e Å^−3
146 parameters	Δρmin = −0.24 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0098 (10)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cl	0.23690 (9)	0.33499 (8)	0.007812 (18)	0.0752 (2)
F	−0.2126 (2)	0.16109 (18)	−0.01121 (4)	0.0768 (4)
N	0.0970 (2)	0.1474 (2)	0.20009 (6)	0.0526 (4)
C1	0.0272 (3)	0.1607 (2)	0.14549 (6)	0.0469 (4)
C2	0.1567 (3)	0.2408 (2)	0.10776 (6)	0.0508 (4)
H2	0.2980	0.2940	0.1180	0.061*
C3	0.0741 (3)	0.2409 (2)	0.05517 (6)	0.0522 (4)
C4	−0.1356 (3)	0.1627 (2)	0.04033 (7)	0.0556 (5)
C5	−0.2655 (3)	0.0829 (3)	0.07672 (8)	0.0594 (5)
H5	−0.4065	0.0299	0.0662	0.071*
C6	−0.1834 (3)	0.0825 (2)	0.12925 (7)	0.0531 (4)
H6	−0.2707	0.0289	0.1542	0.064*
C7	0.2863 (3)	0.2076 (2)	0.21913 (7)	0.0526 (4)
H7	0.3813	0.2671	0.1969	0.063*
C1'	0.3642 (3)	0.1879 (2)	0.27521 (6)	0.0464 (4)
C2'	0.2266 (3)	0.1038 (2)	0.31055 (7)	0.0530 (4)
H2'	0.0824	0.0589	0.2987	0.064*
C3'	0.3038 (3)	0.0869 (3)	0.36310 (7)	0.0603 (5)
H3'	0.2115	0.0304	0.3865	0.072*
C4'	0.5174 (3)	0.1535 (2)	0.38112 (7)	0.0578 (5)
H4'	0.5676	0.1435	0.4167	0.069*
C5'	0.6561 (3)	0.2345 (3)	0.34642 (7)	0.0590 (5)
H5'	0.8006	0.2784	0.3585	0.071*
C6'	0.5807 (3)	0.2506 (3)	0.29361 (7)	0.0564 (4)
H6'	0.6759	0.3038	0.2702	0.068*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl	0.0817 (4)	0.1006 (5)	0.0448 (3)	0.0019 (3)	0.0146 (2)	0.0118 (2)
F	0.0834 (8)	0.1009 (10)	0.0433 (6)	0.0094 (6)	−0.0146 (5)	−0.0051 (5)
N	0.0523 (8)	0.0650 (9)	0.0402 (7)	−0.0025 (6)	0.0026 (6)	0.0031 (6)
C1	0.0507 (9)	0.0504 (8)	0.0396 (8)	0.0052 (7)	0.0023 (7)	0.0007 (6)
C2	0.0494 (9)	0.0596 (10)	0.0431 (8)	0.0005 (7)	0.0020 (7)	−0.0010 (7)
C3	0.0595 (10)	0.0588 (10)	0.0386 (8)	0.0101 (8)	0.0060 (7)	0.0012 (7)
C4	0.0630 (10)	0.0615 (10)	0.0409 (9)	0.0133 (8)	−0.0067 (7)	−0.0048 (7)
C5	0.0525 (9)	0.0659 (11)	0.0580 (10)	0.0001 (8)	−0.0087 (8)	−0.0030 (9)
C6	0.0494 (9)	0.0591 (10)	0.0507 (9)	0.0001 (7)	0.0029 (7)	0.0028 (8)
C7	0.0549 (9)	0.0621 (10)	0.0411 (9)	−0.0023 (8)	0.0056 (7)	0.0042 (7)
C1'	0.0486 (8)	0.0508 (9)	0.0398 (8)	0.0019 (6)	0.0034 (6)	−0.0011 (6)
C2'	0.0511 (9)	0.0648 (10)	0.0431 (9)	−0.0090 (7)	0.0039 (7)	−0.0024 (7)
C3'	0.0686 (11)	0.0714 (11)	0.0416 (9)	−0.0126 (9)	0.0089 (8)	0.0019 (8)
C4'	0.0694 (11)	0.0634 (11)	0.0393 (8)	0.0037 (8)	−0.0053 (8)	−0.0035 (7)
C5'	0.0505 (9)	0.0670 (11)	0.0580 (10)	−0.0023 (8)	−0.0064 (8)	−0.0045 (9)
C6'	0.0517 (9)	0.0655 (11)	0.0522 (10)	−0.0073 (8)	0.0053 (7)	0.0043 (8)

Geometric parameters (Å, º)

Cl—C3	1.7310 (18)	C5—C6	1.380 (2)
F—C4	1.349 (2)	C7—C1'	1.466 (2)
N—C7	1.249 (2)	C1'—C6'	1.387 (2)
N—C1	1.416 (2)	C1'—C2'	1.394 (2)
C1—C6	1.388 (2)	C2'—C3'	1.379 (2)
C1—C2	1.395 (2)	C3'—C4'	1.380 (3)
C2—C3	1.382 (2)	C4'—C5'	1.376 (3)
C3—C4	1.377 (3)	C5'—C6'	1.382 (2)
C4—C5	1.370 (3)
C7—N—C1	122.06 (15)	C4—C5—C6	118.90 (17)
C6—C1—C2	118.98 (15)	C5—C6—C1	121.14 (17)
C6—C1—N	116.15 (15)	N—C7—C1'	122.41 (16)
C2—C1—N	124.84 (15)	C6'—C1'—C2'	118.89 (15)
C3—C2—C1	119.75 (16)	C6'—C1'—C7	119.82 (15)
C4—C3—C2	119.88 (16)	C2'—C1'—C7	121.28 (15)
C4—C3—Cl	119.99 (13)	C3'—C2'—C1'	120.18 (16)
C2—C3—Cl	120.11 (14)	C2'—C3'—C4'	120.29 (17)
F—C4—C5	119.31 (17)	C5'—C4'—C3'	120.01 (16)
F—C4—C3	119.33 (17)	C4'—C5'—C6'	119.99 (16)
C5—C4—C3	121.34 (16)	C5'—C6'—C1'	120.60 (16)